Finishing coated metal surfaces



Patented Nov. 19, 1940 UNITED STATES PATENT. OFFICE- j I 2.22am rmsnmc cosrsn METAL. scnrsoss MauriceD. German, Detroit, Mich, assignor to Sno-Flake Products Company, Detroit, Micln, a corporation of Michigan No Drawing.

ApplicationFebruary 13,1939, I l 1 Serial No. 256,221

2 Claims. (01. 51-4281 of metal and other objects has long been a 10 problem, particularly where a finishing coat is later to be applied. I'he securing of a smooth finish on metal surfaces is diificult, due in part to the waves and other undesirable defects in such surfaces, caused by'rolling or joining of two 15 pieces of metal together as by welding or soldering and the covering of other distinguishable surface fiaws produced during the assembly ofdinarily smoothed by hand or mechanically, em-

ploying an abrasive fixed on a fabric or paper backing. It is a well known fact that it is natural for the hand to follow the original contours of so the surface and the use of hand sanding does not always eliminate the depressed areas or natural waves, particularly when large areas are to be brought to a plane surface for the application of a finish coat. In addition to this-the as use of an abrasive fixed to a permanent backing frequently results in individual scratches of such depth that they are visible after the'finish'coat has been applied. A movable particle of abrasive will not cut as deeply as the 'same particle 4o firmly affixed to a backing material and it has.-

been sought to take advantage. of this fact by the use of water-in-oii emulsions of various yp s in which an abrasive was included, the emulsion being applied to the. coated surface to be smoothed and a mechanical means being employed in an endeavor to level down the surface.

55 I have now found that the foregoing disad "The abrading and leveling of coated surfaces" vantages are obviated and coated metal surfaces satisfactorily abraded and leveled by applying a petroleum distillate-free,- water-dispersive composition, containing a relatively finely divided abrasive, to the coated surface; then mechan- 5 ically abrading down and leveling the surface as with a polishing wheel; and thereafter wate r washing, as by a spray or sponging, the sotreated surface to remove substantially therefrom the residual product of the abrading step '10 before it has appreciably dried. This residual product will comprise the unused portion of the i abrasive composition applied, that portion of the coating which has been cut away by the action of the abrasive, and may include reaction prod- 15 note of the abrasive composition with the coating. a

This improved process results in a uniformly smooth surface free from pits, scratches, and other blemishes and devoid of oily .films and 20 residues of a nature prejudicial to the application of additional layers or coats of finishing enamel, lacquer and the like.

An essential step, according to my invention, is the water-washing of the treated surface to. 85 remove the residual product of the abrading step before it has appreciably dried. In order to accomplish satisfactorily this step, it is necessary that the actual abrading step be carried out at' such' a rate that the residue retains a substanas tial amount of water while in contact with the surface under treatment. 'Once dried, this residue is dimcult to remove. My process is essentially-awet-grinding process and it is desirable that the surface to be abraded and leveled be to thoroughly water-wet before the abrasive composition is'applied thereto. However, where it is expedient to have a dry coated surface, the composition may be diluted with sufiicient water so that the actual abrading step will be carried to out in the-presence of sufficient moisture betermed a wet-grind.

As a suitable abrading composition, we may employ a material consisting essentially of a relatively 'finely' divided abrasive, a water-solu- Allv ble detergent, and'water. Preferably a bodying agent is used. The quantities of the aforesaid materials are 'in such proportions that the com! position is relatively viscous or weakly adhesive and is adapted to be readily applied to and re- 60 tained on the coated surface to be leveled or on the working surface of a mechanical polishing means. In certain instances, it is desirable to employ an anti-foaming agent in the composition and in other instances. a hygroscopic substance 55 50 per cent, which will be present in the final used in the preparation of my composition are:

or a wetting agent may be incorporated in the composition. The proportions of the ingredients are not extremely critical but theabrasive should be in the order of between 80 and 325 screen mesh particle size. Thedetergent must be completely water-dispersive and of sufdcient body to serve both as a lubricant and binding agent in the composition. This latter statement with respect to the detergent is particularly true where a bodying agent such as bentonite is not employed in the preparation of the composition.

A representative composition particularly suitable for use in leveling filler coat on automobile bodies contain betweenabout 55 and 80 parts by weight of an emery powder of about 120-220 mesh; between about 3 and about 5 parts of an alkali metal higher fatty acid soap, such as sodium oleate-stearate and between about 0.2 and about 0.5 parts of bentonite; together with sumcient water to produce a relatively viscous paste, e. g., from 15-30 parts. The compounding of the foregoing composition is ordinarily carried out by thoroughly intermixing the abrasive substance, bodying agent, and soap, in the presence of a portion of the water, e. g.,

terial, stretched over a spongy base, such as rubber, sponge rubber, or felt pad. The preferred speed of the wheel is dependent in part on the hardness of the coating to be leveled, for example, speeds of about 900 R. P. M. may be employed on relatively.highly pigmented coats while speeds ranging up to 1760 R. P. M. may be used on low pigmented coats.

Among the abrasive materials which may be emery, silicon carbide, aluminum oxide, and the like.' The sodium and potassium soaps of fatty acids such as eleic, stearic, lauric, and the like,

are useful as detergent substances, although I gum tragacanth or starch may be saibstitutecl therefor. Where lacquer base or other difficultly wettable coatings are to be leveled, it is advanvtageous that a wetting agent such assulphite pulp waste liquor, alcohol, or similar product be incorporated, generally in amount ranging up to 1 to 2 per cent by weight of the composition. Along with such wetting agent a hygroscopic or evaporation retarding material such as glycerol,

ethylene glycol, diethylene glycol, and the like. may be incorporated in amount up to 3 per cent by weight. This results in such a reduction of the evaporation rate of moisture from the composition as prevents the setting up or hardening of residual abrasive prior to the water-washing step. Anti-foaming agents such as pine oil and the likemay be employed if desired.

My process provides a rapid and economical way of abrading and leveling'down coated surfaces and eliminates the disadvantages inherent in the hand or mechanical abrading of such surfaces with a fixed abrasive.

Compositions prepared within the foregoing proportions have been employed in processing coatings on automobile bodies in commercial production in' accordance with the method herein set forth.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the method herein disclosed, provided the means stated by any of the following claims or the equivalents of such stated means be employed.

I therefore particularly point out and distinctly claim as my invention:

1. The method of smoothing and leveling the surface of a highly pigmented pre-coating on an automobile body which comprises applying a petroleum distillate-free composition containing relatively finely divided abrasive, a water-soluble agent having a weak adhesive and a detergent effect, and water to said coated surface, mechanically abrading down and leveling the coating on said metal surface utilizing a power-driven tool, and thereafter water-washing the coated surface to remove the residual product of the abrading step'before it has appreciably dried.

2. The method of smoothing and leveling the surface of a highly pigmented pro-coating on an automobile body which comprises applying a petroleum distillate-free composition containing relatively finely divided abrasive, a water-soluble agent having a weak adhesive and a detergent effect, and water to said coated surface, mechanically abrading down and leveling the coating on said metal surface utilizing a power-driven wheel of which the contact surface is a fairly rough textile material backed by a resilient base, and thereafter water-washing the coated surface to remove the residual product of the abrading step before it has appreciably dried.

MAURICE D. GERMAN. 

